Transportation of bulk cargo from warm humid climates to temperate zones having lower temperatures and humidity usually results in moisture condensation within the container interior caused by temperature differences between the interior and exterior of the container particularly when the cargo is loaded at elevated temperature and humidity conditions. Condensed water will be deposited on the cargo when the temperature and humidity differences will produce condensation inevitably resulting in claims due to water damage, mold growth, and oxidation depending upon the nature of the bulk cargo being shipped.
As one example of a persisting problem that has occurred due to inadequate ventilation is the experience with condensation experienced when transporting cocoa beans from Caribbean locations to North America. Other commodities will produce similar problems when the bulk cargo may readily experience a loss of moisture to the environment within the interior of a container that is sealed and lacks suitable ventilation. The water or moisture usually condenses on the interior of the container on the roof and side walls eventually precipitating on the product, such as cocoa beans causing stains, mold, growth and other damage that inevitably leads to losses and the filing of claims.
In the conventional sealed cargo container, a "pumping" cycle occurs and functions whenever the ambient temperature falls below that of the cargo load which usually has a temperature ranging from 80 to 90 degrees F. The "pumping" cycle is the occurrence of air currents that circulate above the cargo and beneath the roof of the container when the ambient air is lower than the temperature of the product which contains moisture at the elevated temperature level. By reference to a psychometric chart, one may readily determine the relative humidity at prescribed temperatures and dry bulb and wet bulb conditions. When cooler air permeates the atmosphere, the temperature of the roof and sides of the container will be lowered promoting the conditions requisite for condensation to occur. As the cooler air settles on the top of a load of product where the temperature and relative humidity are higher, the cool air in the container will be warmed and the relative humidity decreased which permits the air to accept additional moisture from the cocoa beans. This warm moist air rises and contacts the cooler container surfaces where condensation occurs. This cycle will repeat itself depending upon the conditions that prevail throughout the transportation of the cocoa beans, and substantial quantities of condensate on the roof and walls precipitate on the product resulting in stains, damage and other deleterious effects prior to unloading.
Attempts have been made to overcome the condensation problems by numerous methods and structures including the provision of forced circulation of which U.S. Pat. No. 4,143,588 is but one example of an active system and U.S. Pat. No. 3,319,349 exemplifies another system that is passive. Both systems illustrated in the aforementioned patents and others are costly to install and may require substantial expenditures for new installation.